Background Systems thinking is a holistic approach that puts the study of wholes before that of parts. It does not try to break systems down into parts in order to understand them; instead, it focuses attention on how the parts act together in networks of interactions. Purpose This study explored the development of holistic school leadership— an approach where principals lead schools through the systems thinking concept and procedures— over principals’ different career stages, a topic that has received little research attention. Research Design Qualitative data were collected via 82 semistructured interviews, six focus groups, and 27 observations of three groups of principals: (a) prospective principals— 24 students attending three principal preparation programs; (b) novice principals— follow-up on 11 prospective principals during their first year after appointment; and (c) experienced principals— eight principals holding that position for 5+ years. Data analysis was conducted by generating themes through an inductive process of condensing, coding, categorizing, and theorizing. Findings Data analysis indicated that the development of systems thinking in school leaders consists of five stages: (a) preservice stage, typified by an expansion of view; (b) survival stage, typified by a slowdown in the development of systems thinking; (c) consolidation stage, typified by a gradual development of systems thinking; (d) role maturity stage, typified by a systemic view; and (e) possible decline stage, typified by some degree of difficulty to think systemically. Conclusions Systems thinking is not equally applicable to aspiring, novice, midcareer, and veteran school principals. This study's findings may help identify ways to enhance and accelerate the development of systems thinking in prospective and currently performing principals in a way that is compatible with the unique features and context of their specific stage.